The effect of climate change on the world's fish is becoming a global issue.
Overfishing may still get the blame for shortages but there is increasing evidence that many species are increasingly affected by climate change, specifically warmer water.
And that has a knock-on effect on the fishing industry.
Marine scientists and fish experts from around the world are in conference at Queen's University, Belfast to discuss the latest situation and share their research.
The focus of their attention is the warming of fish habitats. As the earth slowly warms up, some aquatic ecosystems (oceans, seas, lakes and rivers) have warmed up faster.
Some evidence suggests that parts of the North Sea, for example, may have increased by more than 1C in the past 30 years.
Such a rise in sea temperatures can have a dramatic effect on fish.
Warm-water southern fish are becoming increasingly abundant in northern waters while cold-adapted northern fish appear to have shifted further North and to deeper water to escape warming.
Scientists have discovered that climate change has also affected the timing of fish migrations. In some species the timing has shifted by up to two months.
That is enough to have a substantial affect on the survival of young fish and on fisheries capture rates.
Dr Chris Harrod is lecturer in Fish and Aquatic Ecology at Queens University and organiser of the week's conference.
He says: "Although the decline in many valuable fish stocks is largely a reflection of fishing pressure, fluctuations in some exploited warm-water species, such as the sardine, have been closely related to changing water temperature."
As waters heat up and ecosystems change, fish populations are altering in size and distribution and this will lead to big changes for the fishing industry.
Fish that specifically favour temperature cold water habitats are already showing signs of the struggle with climate change.
John Magnuson, University of Wisconsin, says that cold water fish like trout and charr are affected.
"We already have evidence that they are beginning to show poor performance and in many streams in the European and North American area, we have major declines in the abundance and distribution of these cold water species."
Some seas have already been modified as habitats through temperature change and are stressing their indigenous species.
Hans Portner of the Alfred Wegner Institute in Germany claims that the evidence is very widespread.
"In the southern part of the North Sea we see a process we could call to some extent a 'Mediterranisation'.
"The cold water species like cod are moving out and the warm water species are moving in instead."
He says that in some specific areas the numbers of species is dropping.
"In the Wadden Sea, which has been designated a heritage site, we have a decline in fish biodiversity but this may only be a transitional stage because there may be other species moving in and taking over."
"Northern Ireland is of particular interest", says Chris Harrod.
"Many of the fish there, often referred to as glacial relics, are cold water species which are adapted to the colder conditions of more northern latitudes.
"As our waters heat up these cold-adapted fish such as Atlantic salmon, Arctic charr and pollan are under particular threat.
"Populations that depend on these fish and value them for their biodiversity will also have to adapt to change.
"Many of our species can be considered to be losers under future climate warming scenarios, but there will also be some winners.
"These include the non-native and 'introduced' freshwater fishes, such as the roach that will thrive as waters warm, increasing their impact in lakes such as Lough Neagh," he said.
Lough Neagh is the largest body of freshwater in the UK.
The population of species such as pollan and eels that live in the lough already show signs of decline.
Dr Harrod explains that if the change is related to climate change, that could have both a positive and a negative influence.
"Eels, a species that is very important to Lough Neagh and its surrounding communities, are likely to get bigger as waters get warmer.
"However, the downside may be that changes to marine currents will result in a reduced supply of juvenile eels from the Sargasso Sea to Irish shores."
But for some fish species the effects of climate change could be terminal.
Certain species react to temperature change by massive gender swings.
As the water warms up the embryos are almost all male which has a devastating effect on species survival.
Other species are simply trapped. Those that live in the coldest waters near the poles will have nowhere to escape to as the water slowly warms.
Much of the change could happen in our lifetime.
Often there is little we can do but watch and one of the major concerns raised at the conference is the need for long-term monitoring.
Without it, the current shifts of species and fish population wouldn't have been recognised. But, at the moment, selling that concept to cash-strapped governments around the world will not be easy.